OP - I have been in the same boat as you as per my reply a while back. Sold my G80 back in January, and was searching for some time.
Wanted to report back my experience:
Test drove a bunch of cars, didn't really like anything. I was so close to just purchasing another G80 because in the price bracket, its very.... very tough to beat.
I test drove both a PDK and a manual 718 GT4, they were about $25k more than a g80 (based on my build, not MSRP vs MSRP), of course the GT4s were used with about 15k~ miles or so. Some were tracked, which that's where if you want a super clean GT4, you might be looking in the 130s. For me personally, too much for that car.
I loved the GT4s, but there is one thing I don't like and its the gearing... as you probably have heard in many videos. The gearing is long and its an NA engine, so you really don't get any power until higher up in the revs, which is fine, but then it becomes a struggle to stay within the power band on the street.
I test drove both iterations, a PDK and a manual, both had the same issue. I was just going to say f it... and just pull the trigger and then randomly ran into a 718 GTS 4.0 with the deman gearing...
and holy shit, it absolutely transforms the car. When I first saw it for sale, it bugged me that it "wasn't a GT4" but when I got to drive it, I did not care. I ended up getting the GTS 4.0 and I absolutely love it.... but its a completely different experience than the G80. The G80 was a rocket.
Not saying the 718 is not fast, but don't expect it to be "G80 Fast"
but its damn fun!
TLDR - If you want to make a switch, it's going to be a completely different experience, but make sure you test drive them. I for one felt underwhelmed by the GT4, the regearing makes a world of difference. G80 is a hell of a car, tough to beat for the price.